My girlfriend told me that she replaced her 2004 Chevrolet Malibu'* gas cap with an aftermarket locking one after a few cars near her had their gas siphoned out in the middle of the night.

Since then, though, her car has constantly set the P0455 code (huge EVAP leak). I reset the code for her, but the check engine light keeps coming on.

I looked at her cap, and the thread pattern matches her factory one. I told her to take the cap back to Pep Boys and exchange it, thinking it was a bad cap, but she'* on her second one now, and the code keeps getting set. Any ideas? Can she have her locking fuel cap or not?

(If I had a tuner, I'd delete that code, but I can't, so I'm asking you guys. )

you try putting the original one back on to be sure? if its the cap make sure the rubber o-ring is there like the original. if not try a different brand, i had just a walmart one on my old 03 monte and never gave me issue.